【作者】 李佳；

【导师】 丁选明；

【作者基本信息】 重庆大学 ， 土木工程， 2021， 硕士

【摘要】 桩基础在我国是应用最为广泛的地基加固方法,而且基桩形式多种多样,其中螺纹类桩相较于其他桩型单桩承载力高、适应性强、适用范围广、环保、经济效益显著,所以目前在国内已经应用较为广泛。螺钉桩是本课题组自主研发的一种新型螺纹类桩型(ZL201410723263.5),单桩承载力高。对螺钉桩这一新型桩的承载特性以及截面计算进行研究有助于揭示螺钉桩的承载机理。本文对螺钉桩截面进行了几何分析,通过透明土模型试验,结合数值模拟计算方法,探究了螺钉桩单桩竖向承载特性,讨论了桩身结构参数对承载特性的影响,主要的工作和成果如下:(1)对螺钉桩截面进行几何分析,得到了螺钉桩截面面积、周长、惯性矩的计算公式,并结合Mathematica软件的计算功能讨论了螺钉桩结构参数对截面几何的影响规律。分析结果表明,螺钉桩截面面积和周长都随内半径、螺牙的厚度和高度的增大而增大,随螺牙间距的增大而减小,并存在两个大小不等的主惯性矩,在本文分析的参数范围内相差13%～72%,且截面几何特性优于传统圆桩。(2)制备了满足试验要求的透明土,利用了3D打印技术制作螺钉模型桩,设计了螺钉桩单桩承载透明土模型试验方案,开展了9种工况的室内模型试验,获得了桩顶沉降位移与荷载关系曲线,同时通过PIV技术处理试验中采集的散斑场图像,分析了桩周土体的位移场。试验结果表明,螺钉桩单桩承载能力相较圆桩明显提高,其桩周土体的位移场范围大于圆桩;桩侧土颗粒与螺牙相互咬合使得土体产生剪切变形,发挥出抗剪强度,提高了桩侧阻力;螺钉桩桩身倾斜度增大承载力增大,螺牙间距在最优取值时承载力较大,螺牙高度增大承载力显著提高,而螺牙厚度对承载能力的影响较小。(3)通过PLAXIS有限元软件建立轴对称模型,模拟了螺钉桩单桩承载过程,对比验证了模型建立的正确性,分析了桩身轴力、桩侧阻力、桩土界面应力以及桩周土体剪应力分布情况,讨论了桩身结构参数的影响。结果表明,螺钉桩桩侧阻力较大,进而显著提高了单桩极限承载力;螺牙下端面桩土界面应力较大,其下侧土体产生了较大的剪应力,发生了剪切变形,发挥了土体抗剪强度;当桩身倾斜角取为0.5°～1°时能提高材料利用率,当平均半径与螺牙间距比值为1.3～2.0时,极限承载力较大,机械咬合作用发挥更充分;螺牙高度占桩顶外径比例提高13%,极限承载力提高了23%;螺钉桩螺牙厚度对其单桩承载力的影响较小。更多还原

【Abstract】 Pile foundation is the most widely used method of foundation reinforcement in my country,and there are many types of foundation piles.Threaded piles has been widely used in China for higher bearing capacity,strong adaptability,wide application range,environmental protection and significant economic benefits when compared with traditional piles.The screw pile is a new type of threaded pile(ZL201410723263.5)independently developed by this research group,with high bearing capacity of a single pile.Research on the bearing characteristics and cross-section calculation of the new type of screw pile is helpful to reveal the bearing mechanism of screw pile.In this paper,a geometric analysis of the cross section of the screw pile is carried out,and combined transparent soil model tests with numerical simulation calculation methods to explore the vertical bearing characteristics of a single screw pile and discuss the influence of the structure parameters of the pile.The main work and results of this paper as follows:(1)The geometric analysis of the screw pile cross-section is carried out,and the calculation formulas of the area,circumference,and moment of inertia of cross-section are obtained.Using the Mathematica software,the influence law of the structure parameters of the screw pile on the section geometry is discussed.The results show that the cross-sectional area and circumference of the screw pile increase with the increasing of the radius,the thickness and height of the screw thread,and decrease with the increasing of the screw pitch.And there are two main inertia moments that differ by 13%to 72% within the parameters analyzed in this paper.What’s more,the cross-section geometric characteristics of screw pile are better than traditional round piles.(2)Transparent soil that meets the test requirements is prepared.Screw model piles are made by 3D printing technology.A model test plan for single screw pile bearing capacity based on transparent soil is designed.Model tests under 9 working conditions are carried out indoor to obtain the relationship curve of settlement and load.At the same time,the speckle field images collected in the test are processed by PIV technology to analysis the displacement field of the soil around the pile.The test results show that the bearing capacity of a single screw pile is significantly higher than that of a round pile,and the displacement field of the soil around the pile is larger than that of the round pile.The soil particles on the side of the pile and the screw teeth interlock to cause the soil producing shear deformation and exerting resistance.The soil shear strength increases the pile side resistance.The increasing of the inclination of pile increases the bearing capacity.The bearing capacity is larger when the screw pitch is optimally selected.The bearing capacity increases significantly with thread height increasing,while is less affected by thread thickness increasing.(3)The bearing process of a single screw pile is simulated based on establishing an axisymmetric model by PLAXIS finite element software.The correctness of the model is verified by comparison.The axial force of the pile,the resistance of the pile,the stress of the pile-soil interface,the shear stress of the soil around the pile are obtained.The law of influence of the pile structure parameters is discussed.The results show that the side resistance of the screw pile is large,which significantly increases the ultimate bearing capacity of the single pile.The pile-soil interface stress at the lower surface of the screw thread is relatively large,so that the soil underneath has a large shear stress and shear deformation to exert the shear strength of the soil.When the inclination angle of the pile is 0.5°～1°,the material utilization rate can be improved.When the ratio of the average radius to the thread pitch is 1.3～2.0,the ultimate bearing capacity is larger because of the fully exerted mechanical occlusion.When the proportion of the thread height to the outer diameter of the pile top is increased by 13%,the ultimate bearing capacity is increased by 23%.The thickness of the thread has a smaller effect on the bearing capacity of a single pile.更多还原